Two-element eyepiece

ABSTRACT

A two-element eyepiece having a biconvex singlet with the radii of the convex surfaces being substantially identical and a convex-plano doublet formed of a biconvex element having radii of the convex surfaces being substantially equal with a concavo-plano component cemented thereto, has a field of view of approximately 40° with good correction for normal eyepiece aberrations. Eye relief is approximately 80 percent of the effective focal length.

BACKGROUND OF THE INVENTION

This invention relates to microscope eyepieces and more particularly, relates to an eyepiece having a magnification of substantially 10X, an apparent field of view of approximately 40°, eye relief equal to approximately 80 percent of the effective focal length and a minimum number of elements having configurations desirable to minimize production costs is advantageous.

It is an object of this invention to provide 10X eyepieces having elements of a configuration desirable for minimizing production costs.

It is another object of the present invention to provide an inexpensive 10X eyepiece having good correction for the usual eyepiece aberrations of field curvature, distortion and lateral color.

It is still further an object of the present invention to correct pupil aberrations to reduce annoying shadows resulting from slight head movements to a minimum.

THE DRAWING

The drawing is an optic 1 diagram of an eyepiece view transversed to the optical axis.

DETAILED DESCRIPTION OF THE INVENTION

Referring to the drawing, an eyepiece X, is shown diagrammatically with optically-aligned lenses I and II. The first element I is a biconvex positive singlet with radii R₁ and R₂ being substantially equal, and the second element II is a convex-plano positive doublet. Doublet II consists of a biconvex singlet, having radii R₃ and R₄ being substantially equal, cemented to a concavo-plano singlet. The eyepiece has an eye relief of approximately 80 percent the effective focal length which is adequate for viewing with or without glasses.

The parameters of an eyepiece according to the present invention are set forth in Table I with the axial thicknesses of successive lens elements designated T₁ to T₃, the successive axial spaces from the eyepiece focal plane FP to the observer's eye designated S₀ to S₂ , successive lens radii are designated R₁ to R₅ where a minus sign (-) applies to surfaces whose center of curvature lies on the focal plane side of their vertices, refractice indices of the successive glasses are designated ND₁ to ND₃ and the Abbe numbers of the successive glasses are designated γ₁ to γ₃.

                                      TABLE I                                      __________________________________________________________________________                               Index of Abbe                                        Lens                                                                              Radius  Thickness                                                                             Space   Refraction                                                                              Number                                      __________________________________________________________________________                       S.sub.O =1.0331x                                                R.sub.1 =1.5796x                                                            I          T.sub.1 =0.2057x                                                                              1.52<ND.sub.1 <1.53                                                                     ν.sub.1 ≅58                       R.sub.2 =-1.5796x                                                                             S.sub.1 =0.02174x                                               R.sub.3 =1.0626x                                                                       T.sub.2 =0.2341x                                                                              1.52<ND.sub.2 <1.53                                                                     ν.sub.2 ≅58                    II R.sub.4 =-1.0626x                                                                      T.sub.3 =0.1087x                                                                              1.78<ND.sub.3 <1.79                                                                     ν.sub.3 ≅25                       R.sub.5 =∞                                                                              S.sub.2 =0.8609x                                             __________________________________________________________________________      where x= 20 to 26mm                                                      

One embodiment of the present invention wherein x has a value of 23.0 has the following values:

                                      Table II                                     __________________________________________________________________________                            Index of                                                                              Abbe                                             Lens                                                                              Radius Thickness                                                                            Space  Refraction                                                                            Number                                           __________________________________________________________________________                     S.sub.O =23.761                                                   R.sub.1 =36.331                                                             I         T.sub.1 =4.738                                                                              ND.sub.1 =1.523                                                                       ν.sub.1 =58.6                                    R.sub.2 =-36.331                                                                            S.sub.1 =0.5                                                      R.sub.3 =24.439                                                                       T.sub.2 =5.384                                                                              ND.sub.2 =1.523                                                                       ν.sub.2 =58.6                                 II R.sub.4 =-24.439                                                                      T.sub.3 =2.50                                                                               ND.sub.3 =1.786                                                                       ν.sub.3 =25.5                                    R.sub.5 =∞                                                                            S.sub.2 =19.8                                                  __________________________________________________________________________

It will be apparent that the foregoing values are variable depending on the value of x. Other forms are thus possible and changes may be made in the values of the constructional data named without departing from the spirit of this invention.

The apparent excess precision implied by the large number of decimal places is somewhat fictitious for a number of reasons. For instance, varying radii (larger in particular) by several millimeters would produce only minimal changes, mostly in focal length. Variations in thicknesses of 0.1 to 0.2mm would not adversely affect performance. In fact, large regions of design exist (assuming that radii and thicknesses are properly balanced). 

What is claimed is:
 1. A two-element eyepiece having a magnification of substantially 10X, a field of view of approximately 40° and eye relief of approximately 80 percent of the effective focal length which comprises a biconvex positive singlet as the first element and a convex-plano positive doublet as the second element, said lens elements having the following values:

    ______________________________________                                                                                  Abbe                                  Lens Radius   Thickness                                                                               Space  Refraction Number                                ______________________________________                                                                S.sub.0 =                                                                      1.0331x                                                      R.sub.1 -                                                                               1.5796x                                                          I             T.sub.1 =                                                                               1.52<ND.sub.1 <1.53                                                                   ν.sub.1 ≅58                                       0.2057x                                                               R.sub.2 = -              S.sub.1 =0.02174x                                     -1.5796x                                                                       R.sub.3 = -                                                                             1.0626x                                                                        T.sub.2 =                                                                               1.52<ND.sub.2 <1.53                                                                   ν.sub.2 ≅58                                       0.2341x                                                          II   R.sub.4 =                                                                      -1.0626x                                                                                T.sub.3 =                                                                               1.78<ND.sub.3 <1.79                                                                   ν.sub.3 ≅25                                       0.1087x                                                               R.sub.5 =∞                                                                                 S.sub.2 = -        0.8609x                              ______________________________________                                          where x= 20 to 26mm  wherein the minimum amount of surface curvatures and      lens elements provide good correction for field curvature, distortion and      lateral color aberrations.


2. The eyepiece according to claim 1 wherein x is 23.0mm, ND₁ is 1.523, ND₂ is 1.523, ND₃ is 1.786, γ₁ is 58.6, γ₂ is 58.6 and γ₃ is 25.5. 